The nature of hydrogen stabilization in the reduced copper chromites

In situ powder X-ray and neutron diffraction showed that copper chromite retains its spinel structure (space group Fd3m, a = 8.348(3) Angstrom) in hydrogen at 320 degrees C. The spinel has a copper ion deficiency and is stabilized by the dissolved hydrogen. Two hydrogen states are observed in the spinel structure: as specific hydrogen species H (16c interstitial position) and as OH groups with covalent bounding (32e crystallographic position). The hydrogen species bonded to the lattice oxygen is formed as a result of the exchange interaction between hydrogen atoms and Cu2+ ions. In this case a portion of copper ions are reduced to Cu-0 as flat particles onto the surface; another portion is reduced to Cu1+ and transferred towards the 16c positions.